Dual Processing of R-Loops and Topoisomerase I Induces Transcription-Dependent DNA Double-Strand Breaks.

1. Cell Rep. 2019 Sep 17;28(12):3167-3181.e6. doi: 10.1016/j.celrep.2019.08.041. Dual Processing of R-Loops and Topoisomerase I Induces Transcription-Dependent DNA Double-Strand Breaks. Cristini A(1), Ricci G(2), Britton S(3), Salimbeni S(2), Huang SN(4), Marinello J(5), Calsou P(3), Pommier Y(4), Favre G(6), Capranico G(5), Gromak N(7), Sordet O(8). Author information: (1)Cancer Research Center of Toulouse, INSERM, Université de Toulouse, Université Toulouse III Paul Sabatier, CNRS, 31037 Toulouse, France; Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK. (2)Cancer Research Center of Toulouse, INSERM, Université de Toulouse, Université Toulouse III Paul Sabatier, CNRS, 31037 Toulouse, France; Department of Pharmacy and Biotechnology, University of Bologna, 40126 Bologna, Italy. (3)Institut de Pharmacologie et Biologie Structurale, IPBS, Université de Toulouse, CNRS, UPS, Equipe Labellisée Ligue contre le Cancer 2018, 31077 Toulouse, France. (4)Developmental Therapeutics Branch and Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD, USA. (5)Department of Pharmacy and Biotechnology, University of Bologna, 40126 Bologna, Italy. (6)Cancer Research Center of Toulouse, INSERM, Université de Toulouse, Université Toulouse III Paul Sabatier, CNRS, 31037 Toulouse, France. (7)Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK. Electronic address: natalia.gromak@path.ox.ac.uk. (8)Cancer Research Center of Toulouse, INSERM, Université de Toulouse, Université Toulouse III Paul Sabatier, CNRS, 31037 Toulouse, France. Electronic address: olivier.sordet@inserm.fr. Although accumulation of DNA damage and genomic instability in resting cells can cause neurodegenerative disorders, our understanding of how transcription produces DNA double-strand breaks (DSBs) is limited. Transcription-blocking topoisomerase I cleavage complexes (TOP1ccs) are frequent events that prime DSB production in non-replicating cells. Here, we report a mechanism of their formation by showing that they arise from two nearby single-strand breaks (SSBs) on opposing DNA strands: one SSB from the removal of transcription-blocking TOP1ccs by the TDP1 pathway and the other from the cleavage of R-loops by endonucleases, including XPF, XPG, and FEN1. Genetic defects in TOP1cc removal (TDP1, PNKP, and XRCC1) or in the resolution of R-loops (SETX) enhance DSB formation and prevent their repair. Such deficiencies cause neurological disorders. Owing to the high frequency of TOP1cc trapping and the widespread distribution of R-loops, these persistent transcriptional DSBs could accumulate over time in neuronal cells, contributing to the neurodegenerative diseases. Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved. DOI: 10.1016/j.celrep.2019.08.041 PMCID: PMC8274950 PMID: 31533039 [Indexed for MEDLINE]